US20100060284A1

US20100060284A1 - Magnetic resonance imaging apparatus and control method of magnetic resonance imaging apparatus

Info

Publication number: US20100060284A1
Application number: US12/555,946
Authority: US
Inventors: Satoshi Sugiura
Original assignee: Toshiba Corp; Toshiba Medical Systems Corp
Current assignee: Canon Medical Systems Corp
Priority date: 2008-09-09
Filing date: 2009-09-09
Publication date: 2010-03-11
Also published as: US8188743B2; CN101669822A; CN101669822B; JP2010088870A; JP5582739B2

Abstract

According to a Magnetic Resonance Imaging (MRI) apparatus, each of buttons provided in a plurality of sections included in a receiving coil receives from an operator a selecting operation of selecting a section in which the button itself is provided. A control unit of a computer system moves a table on which a subject is placed such that the center of the section selected by receiving the selecting operation via the button is positioned at the center of a magnetic field.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2008-230994, filed on Sep. 9, 2008, and No. 2009-172049, filed on Jul. 23, 2009; the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a magnetic resonance imaging apparatus that images the inside of a subject by using a magnetic resonance phenomenon, and a control method of the magnetic resonance imaging apparatus. The present invention particularly relates to a technology for easily setting a table on which a subject is placed to a target position.
2. Description of the Related Art
A magnetic resonance imaging method is a method of acquiring chemical and physical microscopic information about a substance by using a magnetic resonance phenomenon. The magnetic resonance phenomenon is a phenomenon that when being placed in a magnetic field, an aggregation of subject nuclear spins resonates with a radio-frequency magnetic field in which each atomic nucleus spins at a particular frequency (resonance frequency) responding to its own unique magnetic moment and an existing magnetic field, and generates a signal (magnetic resonance signal) in a relaxation process.
A magnetic resonance imaging apparatus using such magnetic resonance imaging method needs to position a receiving coil for receiving a magnetic resonance signal and the center of a magnetic field that is to be a reference when applying a gradient magnetic field. In other words, matching the center of the receiving coil to the center of the magnetic field is a requirement to obtain a highly accurate Magnetic Resonance (MR) image.
The reason for this is because a static magnetic field generated by a magnet and a gradient magnetic field generated by a gradient magnetic-field coil are both very difficult to be made spatially wholly uniform; uniformity of the static magnetic field and linearity of the gradient magnetic field are made generally ideal at the center, and getting more degraded with the periphery approaching, so that an image taken in the vicinity of the periphery has unsatisfactory fat suppression due to ununiformity of the static magnetic field and image distortion caused by non-linearity of the gradient magnetic field. Such degradation in the image quality often influences a diagnosis if exceeding a certain level.
Conventional positioning of a receiving coil and a table on which a subject is placed, for example, in a case of a coil used as a receiving coil for an abdomen, is performed by a method that, to begin with, the center of the receiving coil is placed on a subject's portion to be scanned, and furthermore, the scan portion is positionally adjusted with a projection light emitted by a projector for positioning, and then the table is moved to the center of a magnetic field. The method needs doubled operations and confirmations, so that it requires time and efforts.
Particularly, a table moving operation of matching a light emitted by the projector with a target position is difficult to perform through only one time of execution of start and stop of a move. Therefore, usually, it is required complicated operations of performing rough setting first, and then switching the movement speed of the table to a low speed, and repeating a fine adjustment of the table forward and backward. If using a projector that uses a laser light, when eyeballs of a subject pass under the projector, an attention needs to be paid, for example, lighting out the projector or instructing the subject to close his/her eyes, in order to protect eyeballs.
If performing a scan by using a coil including a plurality of elements, such as a phased array coil; in order to perform the scan at the most sensitive position for the receiving coil element, and to prevent interference of any signal from an unwanted site, the positions of the coil elements to be used need to be accurately matched with the center of the magnetic field.
To solve such problems, for example, JP-A H7-124135 (KOKAI) discloses a method according to which a marker that generates an MR signal is provided at the center of a receiving coil; the position of the marker is obtained by collecting an MR signal from the marker, and then positioning of the receiving coil is performed. FIG. 15 is a schematic diagram for explaining a conventional method of positioning a receiving coil by using a marker. As shown in the figure, according to the method, an MR signal is collected by applying a readout gradient magnetic field G_R[Hz/cm] of which a magnetic field in the z-axis direction is zero at the center of the magnetic field. As a result, when the frequency of the MR signal collected from the marker is f₀+Δf [Hz] (f₀is the center frequency), a distance d between the center of the magnetic field and the marker is obtained by d=(f₀+Δf−f₀) /G_R[cm].
Moreover, JP-A 2005-124855 (KOKAI) discloses a method of inserting a table on which a subject is placed to a desired position by using a combination of a light emitting element mounted on the upper surface of a receiving coil and a light receiving element mounted at the opening of a gantry. Furthermore, JP H5-65179 (KOKAI) discloses a unit that sets a region of interest on an image displayed on a monitor, and selects one of Radio Frequency (RF) coils. Moreover, JP-A 2007-282735 (KOKAI) discloses a method according to which a light emitting unit for guiding a subject is provided on a receiving coil in use, so that a subject can appropriately follow an instruction from an operator.
However, JP-A H7-124135 (KOKAI) does not propose any unit for an operator to select easily an element to be set at the center of the magnetic field when the receiving coil includes a plurality of elements. Moreover, according to the method disclosed in JP-A 2005-124855 (KOKAI), when a receiving coil includes a plurality of elements, or a plurality of receiving coils are simultaneously installed, a slide amount of the table cannot be set in accordance with the position of an element to be used from among them.
Furthermore, according to the method disclosed in JP H5-65179 (KOKAI), a scan position cannot be specified before collecting any image, so that it is impossible to specify the position of the table prior to a scan, so that an object to eliminate time and effort required in a procedure using a projector when inserting the table cannot be achieved. Moreover, JP-A 2007-282735 (KOKAI) does not propose any unit for the operator to select a receiving element of the RF coil prior to the insertion of the table.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a magnetic resonance imaging apparatus includes a plurality of coils that receives a magnetic resonance signal irradiated from a subject; a receiving coil that includes the plurality of coils; a coil selecting unit that is provided in the receiving coil, and receives from an operator a selecting operation of selecting a coil from among the plurality of coils; and a control unit that moves a table on which the subject is placed such that the coil selected by receiving the selecting operation by the coil selecting unit is positioned at a center of a magnetic field.
According to another aspect of the present invention, a method of controlling a magnetic resonance imaging apparatus, the method includes receiving from an operator a selecting operation of selecting at least one coil from among a plurality of coils included in a receiving coil that receives a magnetic resonance signal irradiated from a subject, and moving a table on which the subject is placed such that the coil selected by receiving the selecting operation is positioned at a center of a magnetic field.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a Magnetic Resonance Imaging (MRI) apparatus according to a first embodiment of the present invention;

FIGS. 2 and 3 are schematic diagrams for explaining conventional positioning of a scan portion;

FIG. 4 is a schematic diagram of a state that a receiving coil is set on a subject on the MRI apparatus according to the first embodiment;

FIG. 5 is a schematic diagram of an appearance of the receiving coil according to the first embodiment;

FIG. 6 is a schematic diagram of an indicator according to the first embodiment;

FIG. 7 is a functional block diagram of the receiving coil and a computer system according to the first embodiment;

FIG. 8 is a flowchart of a flow of positioning of a scan portion performed by the MRI apparatus according to the first embodiment;

FIG. 9 is a schematic diagram of an appearance of a receiving coil according to a second embodiment of the present invention;

FIG. 10 is a flowchart of a flow of positioning of a scan portion performed by an MRI apparatus according to the second embodiment;

FIGS. 11 and 12 are schematic diagrams of a case where the surfaces of elements are caused to emit light;

FIG. 13 is a schematic diagram of a receiving coil arranged on the back side of a subject;

FIG. 14 is a schematic diagram of an example of a receiving coil that includes only one array of elements in the z-axis direction; and

FIG. 15 is a schematic diagram for explaining a conventional method of positioning a receiving coil by using a marker.

DETAILED DESCRIPTION OF THE INVENTION

Exemplary embodiments of a magnetic resonance imaging apparatus and a control method of the magnetic resonance imaging apparatus according to the present invention will be explained below, in detail with reference to the accompanying drawings. A Magnetic Resonance Imaging apparatus is referred to as an MRI apparatus, and a Magnetic Resonance signal is referred to as an MR signal in the embodiments explained below.
First of all, a configuration of the MRI apparatus according to the first embodiment is explained below with reference to FIG. 1. FIG. 1 is a schematic diagram of a configuration of the MRI apparatus according to the first embodiment. As shown in the figure, an MRI apparatus 100 according to the first embodiment includes a static magnetic-field magnet 1, a gradient magnetic-field coil 2, a gradient magnetic-field power source 3, a couch 4, a couch control unit 5, a transmitting coil 6, a transmitting unit 7, a receiving coil 8, a receiving unit 9, and a computer system 10.
The static magnetic-field magnet 1 is formed in a hollow cylindrical shape, and generates a uniform static magnetic field in its inside space. For example, a permanent magnet, or a super conducting magnet is used as the static magnetic-field magnet 1.
The gradient magnetic-field coil 2 is formed in a hollow cylindrical shape, and is arranged inside the static magnetic-field magnet 1. The gradient magnetic-field coil 2 is formed of three coils in combination corresponding to x-axis, y-axis, and z-axis orthogonal to one another. The three coils generate gradient magnetic fields of which field strengths vary along three directions of the x-axis, y-axis, and z-axis, respectively, by individually receiving a current supply from the gradient magnetic-field power source 3, which will be described later. It is assumed that the z-axis direction is the same direction as that of the static magnetic field.
The gradient magnetic fields of the x-axis, y-axis, and z-axis generated by the gradient magnetic-field coil 2 correspond to, for example, a slice-selective gradient magnetic field Gs, a phase encoding gradient magnetic field Ge, and a readout gradient magnetic field Gr, respectively. The slice-selective gradient magnetic field Gs is used for arbitrarily setting a scan cross section. The phase encoding gradient magnetic field Ge is used for changing the phase of a magnetic resonance signal in accordance with a spatial position. The readout gradient magnetic field Gr is used for changing the frequency of an MR signal in accordance with a spatial position.
The gradient magnetic-field power source 3 supplies a current to the gradient magnetic-field coil 2 based on pulse-sequence execution data sent from the computer system.
The couch 4 includes a table 4 a on which a subject P is to be placed, and under the control of the couch control unit 5, which will be described later, the couch 4 inserts the table 4 a on which the subject P is placed, into a hole (a scanning space) of the gradient magnetic-field coil 2. Usually, the couch 4 is installed such that the longitudinal direction of the couch 4 is parallel to the central axis of the static magnetic-field magnet 1.
The couch control unit 5 moves the table 4 a in the longitudinal direction and upward and downward by driving the couch 4.
The transmitting coil 6 is arranged inside the gradient magnetic-field coil 2, and generates a radio-frequency magnetic field by receiving supply of a radio-frequency pulse from the transmitting unit 7.
The transmitting unit 7 transmits a radio-frequency pulse corresponding to a Larmor frequency to the transmitting coil 6 based on pulse-sequence execution data sent from the computer system. The transmitting unit 7 includes an oscillating unit, a phase selecting unit, a frequency converting unit, an amplitude modulating unit, a radio-frequency power amplifying unit, and the like.
The oscillating unit generates a radio-frequency signal of a resonance frequency unique to a subject nucleus in the static magnetic field. The phase selecting unit selects a phase of the radio-frequency signal. The frequency converting unit converts the frequency of the radio-frequency signal output by the phase selecting unit. The amplitude modulating unit modulates the amplitude of the radio-frequency signal output by the frequency converting unit in accordance with, for example, a sinc function. The radio-frequency power amplifying unit amplifies the radio-frequency signal output by the amplitude modulating unit. As a result of operations performed by the above units, the transmitting unit 7 transmits a radio-frequency pulse corresponding to a Larmor frequency to the transmitting coil 6.
The receiving coil 8 is arranged inside the gradient magnetic-field coil 2, and receives an MR signal emitted from the subject P owing to an influence of the radio-frequency magnetic field described above. Specifically, the receiving coil 8 includes a plurality of elements each of which includes a coil for receiving an MR signal, and upon receiving an MR signal with the coil of each element, the receiving coil 8 outputs the received MR signal to the receiving unit 9.
The receiving unit 9 creates MR signal data based on the MR signal output by the receiving coil 8 based on pulse-sequence execution data sent from the computer system. After creating the MR signal data, the receiving unit 9 transmits the MR signal data to the computer system 10.
The computer system 10 performs total control of the MRI apparatus 100, data collection, image reconstruction, and the like. The computer system 10 includes an interface unit 11, a data collecting unit 12, a data processing unit 13, a storage unit 14, a display unit 15, an input unit 16, and a control unit 17.
The interface unit 11 is connected to the gradient magnetic-field power source 3, the couch control unit 5, the transmitting unit 7, and the receiving unit 9; and controls input and output of signals that are given and received between each of the connected units and the computer system 10.
The data collecting unit 12 collects MR signal data transmitted from the receiving unit 9 via the interface unit 11. When the MR signal data is collected, the data collecting unit 12 stores the collected MR signal data into the storage unit 14.
The data processing unit 13 performs post-processing, i.e., reconstruction processing, such as a Fourier transform, on MR signal data stored in the storage unit 14, and creates spectrum data or image data of a desired nuclear spin inside the subject P.
The storage unit 14 stores MR signal data collected by the data collecting unit 12, and image data created by the data processing unit 13, with respect to each subject P.
The display unit 15 displays various information, such as spectrum data or image data created by the data processing unit 13. A display device, such as a liquid crystal display, can be used as the display unit 15.
The input unit 16 receives various operations and information input from an operator. As the input unit 16, a pointing device, such as a mouse or a trackball, a selecting device, such as a mode switch, and an input device, such as a keyboard, can be used as required.
The control unit 17 includes a Central Processing Unit (CPU) and a memory, both of which are not shown, and controls the MRI apparatus 100 overall by controlling each unit described above.
As described above, a general configuration of the MRI apparatus 100 according to the first embodiment has been explained. Prior to further explaining the MRI apparatus 100 below in detail, conventional positioning of a scan portion is explained below first with reference to FIGS. 2 and 3. FIGS. 2 and 3 are schematic diagrams for explaining conventional positioning of a scan portion.
The positioning of a scan portion explained below is setting a portion intended to be scanned in the subject P at the center of a magnetic field by moving the table 4 a at the beginning of an examination after placing the subject P on the table 4 a. The term “the center of a magnetic field” is not limited to one point with the highest uniformity of the magnetic field, but includes a region of a predetermined area in which the uniformity of the magnetic field is higher than a reference. Moreover, explained below is a case of using a receiving coil 18 that includes 16 elements in total arranged in four rows each in the x-axis direction and the z-axis direction, and it is assumed that a scan is performed by using the elements in the third row from the head of the subject P.
According to the conventional positioning, as shown in FIG. 2, the operator places the subject P on the table 4 a that is installed on the couch 4 and movable in the horizontal direction, and then places the receiving coil 18 on a scan target portion, for example, a liver. When placing the receiving coil 18, the operator sets the receiving coil 18 onto the subject P such that the center of a region intended to be scanned in the subject P matches to the center in the table moving direction of a sensitive region of the elements in the third row.
Subsequently, the operator lights a projector la installed on the static magnetic-field magnet 1, and then moves the table 4 a in the z-axis direction, as shown in FIG. 3. The operator then stops the table 4 a once at a position at which a light L projected from the projector 1 a matches with the center of the region intended to be scanned in the subject P. Accordingly, the MRI apparatus 100 recognizes a slide amount of the table 4 a.
The operator then gives an instruction of an automatic slide of the table 4 a to the MRI apparatus 100. When receiving the instruction, the MRI apparatus 100 moves the table 4 a until the point set with the projector 1 a matches to the center of the magnetic field. The above instructions of the lighting of the projector 1 a, and the move, the stop, and the automatic slide of the table 4 a are given by using buttons on an operation panel 1 b.
In this way, the conventional positioning of a scan portion needs an operation of setting the center of the receiving coil onto the scan portion, an operation of positioning by using a projection light of the projector 1 a, and an operation of moving the table 4 a to the center of the magnetic field, and consequently requires time and efforts.
For this reason, the MRI apparatus 100 according to the first embodiment is configured to perform easily positioning of a scan portion and the center of the magnetic field even when using a plurality of coils as a coil that receives a magnetic resonance signal, by eliminating the need for the operation of positioning by using a projection light of the projector 1 a.
Therefore, according to the MRI apparatus 100 according to the first embodiment, a plurality of buttons is provided on the receiving coil 8, and each of the buttons receives from the operator a selecting operation of selecting a coil from among the coils. The control unit 17 of the computer system 10 then moves the table 4 a on which a subject is to be placed such that the coil selected by receiving the selecting operation via the button is positioned at the center of the magnetic field.
The MRI apparatus 100 is explained below in detail mainly about the receiving coil 8 and the computer system 10. First of all, the receiving coil 8 according to the first embodiment is explained below in detail with reference to FIGS. 4, 5, and 6. Although explained below is a case where the receiving coil 8 includes 16 elements in total that are arranged in four rows each in the x-axis direction and the z-axis direction, the number of elements included in the receiving coil 8 is not limited to this.
FIG. 4 is a schematic diagram of a state that the receiving coil 8 is set on the subject P on the MRI apparatus 100 according to the first embodiment. As shown in the figure, the receiving coil 8 is set, for example, on an abdomen of the subject P, and includes 16 elements arranged in four rows each in the x-axis direction and the z-axis direction, similarly to the receiving coil 18 shown in FIG. 2. Hereinafter, each group of elements arranged in parallel in the x-axis direction is called “section”. In other words, the receiving coil 8 according to the first embodiment includes four rows of sections each of which includes four elements.
According to the first embodiment, each section of the receiving coil 8 is provided with buttons 50 a to 50 d for the operator to select coils by section. FIG. 5 is a schematic diagram of an appearance of the receiving coil 8 according to the first embodiment. The figure depicts the upper surface of the receiving coil 8, and a direction extending between the right and the left of the figure corresponds to the z-axis direction. As shown in the figure, the receiving coil 8 includes four rows of sections 40 a to 40 d arranged in the z-axis direction, and each element at one end of each of the sections is provided with a button. Specifically, an element at one end of the section 40 a is provided with the button 50 a; an element at one end of the section 40 b is provided with the button 50 b; an element at one end of the section 40 c is provided with the button 50 c; and an element at one end of the section 40 d is provided with the button 50 d, respectively.
Each of the buttons 50 a to 50 d individually receives from the operator a selecting operation of selecting the section in which the button itself is provided. Specifically, each of the buttons 50 a to 50 d can take a state of ON or OFF individually; and when it is pressed by the operator (when it is turned to the ON state), it causes the receiving coil 8 to hold element selection information indicating that the section in which the button itself is provided is selected by the operator.
Moreover, each of the buttons 50 a to 50 d is provided with an indicator. FIG. 6 is a schematic diagram of an indicator according to the first embodiment. Each of the buttons 50 a to 50 d has the same configuration, so that a configuration of the button 50 a is explained below as an example. As shown in the figure, the button 50 a includes an indicator 60 a.
The indicator 60 a gives notice of a coil selected by receiving a selecting operation via the button 50 a. For example, the indicator 60 a is implemented by a Light Emitting Diode (LED), and lights up when the button 50 a is pressed by the operator (when the button 50 a is turned to the ON state).
In this way, when any of the buttons 50 a to 50 d is pressed, corresponding one of indicators 60 a to 60 d lights up, so that the operator can easily confirm a selected section (element). The indicators 60 a to 60 d are not necessarily provided on the buttons 50 a to 50 d, but can be provided independently in the vicinities of the buttons 50 a to 50 d, respectively.
Relation between the receiving coil 8 and the computer system 10 is explained below with reference to FIG. 7. FIG. 7 is a functional block diagram of the receiving coil 8 and the computer system 10 according to the first embodiment. As shown in the figure, the receiving coil 8 and the computer system 10 exchange various signals each other via a switch 20.
The switch 20 turns the coil of an element selected by the operator from among the elements 70 a to 70 d included in the receiving coil 8 to a state capable to receive a signal, under the control of the control unit 17 of the computer system 10. The switch 20 can be included in, for example, the receiving unit 9.
The receiving coil 8 includes a plurality of elements as described above. FIG. 7. depicts elements 70 a to 70 d provided with the buttons 50 a to 50 d, respectively, from among the elements. The element 70 a includes a coil 71 a, a signal amplifier 72 a, the button 50 a, and the indicator 60 a. The element 70 b includes a coil 71 b, a signal amplifier 72 b, the button 50 b, and the indicator 60 b; and the element 70 d includes a coil 71 d, a signal amplifier 72 d, the button 50 d, and the indicator 60 d. Each of the elements 70 a to 70 d has the same configuration, so that a configuration of the element 70 a is explained below as an example.
The button 50 a is a button for selecting the section that includes the element 70 a, and the indicator 60 a lights up when the button 50 a is pressed. Specifically, when the button 50 a is pressed by the operator, the indicator 60 a lights up, and the receiving coil 8 holds element selection information indicating that the section including the element 70 a is selected.
The element selection information held by the receiving coil 8 is transmitted to the control unit 17 via the interface unit 11 in response to a request from the control unit 17 of the computer system 10. When the element selection information is transferred, the control unit 17 controls the switch 20 such that only coils of elements included in the section selected by the operator are turned capable to receive signals based on the element selection information. The control unit 17 transmits to the switch 20 via the interface unit 11 an element selection instruction of instructing the switch 20 to turn only the coils of the elements included in the selected section capable to receive signals.
The coil 71 a receives an MR signal irradiated from the subject P. The signal amplifier 72 a amplifies an MR signal received by the coil 71 a, and transmits the amplified MR signal to the computer system 10 via the switch 20.
Positioning of a scan portion performed by the MRI apparatus 100 according to the first embodiment is explained below. FIG. 8 is a flowchart of a flow of positioning of a scan portion performed by the MRI apparatus 100 according to the first embodiment. Explained below is a case of performing a scan by using coils of elements included in the section 40 c arranged in the third row from the head of the subject P.
As shown in the figure, according to the MRI apparatus 100 according to the first embodiment, to begin with the receiving coil 8 is set on a scan portion of the subject P by the operator (Yes at Step S101). A section to be positioned at the magnetic field center is then selected by the operator by pressing a button of a section positioned at the center of a region intended to be scanned in the subject P. In this case, the section 40 c is selected by pressing the button 50 c by the operator.
When the section 40 c to be positioned at the magnetic field center is selected (Yes at Step S102), the indicator 60 c of the selected section 40 c lights up (Step S103).
Subsequently, when an instruction of an automatic slide of the table 4 a is given by pressing a button on the operation panel 1 b by the operator (Step S104), the control unit 17 of the computer system 10 requests the receiving coil 8 for element selection information. Accordingly, element selection information is transferred from the receiving coil 8 to the control unit 17 via the interface unit 11 (Step S105).
When the element selection information is transferred, the control unit 17 controls the switch 20 such that only the coils of the elements included in the section 40 c are turned capable to receive signals, based on the element selection information. Accordingly, the coils of the elements included in the section 40 c are turned to a state selected as an element to receive an MR signal.
Subsequently, the control unit 17 starts moving the table 4 a in the z-axis direction (the longitudinal direction of the table 4 a) by controlling the couch control unit 5 (Step S106), and receives an MR signal of the subject P with the coils of the elements included in the selected section 40 c (Step S107).
At Step S107, the MR signal is received in a state as the coil is applied with a gradient magnetic field in the z-axis direction. Therefore, by performing a Fourier transformation of a signal received under the state that the section is in a sensitive region for the transmitting coil 6 by the coil of the element included in the selected section, a distance in the z-axis direction between the center of the selected section and the center of the magnetic field can be measured. The measurement method is basically similar to a method described in detail in JP-A H7-124135 (KOKAI).
According to the first embodiment, although not an MR signal from a marker attached on an element as described in JP-A H7-124135 (KOKAI), but an MR signal irradiated from the subject P is used, there is no fundamental difference in the principles of measurement. When using an MR signal from the subject P, a spectrum obtained through a Fourier transformation extends along the width of the sensitivity region of the receiving element in the z-axis direction. To improve measurement precision, for example, a signal exceeding a threshold higher than a noise component of the spectrum is extracted, and processed through processing of obtaining a half-width.
After that, when receiving an MR signal from which the center position of the section 40 c can be measured (Yes at Step S108), the control unit 17 measures a distance in the z-axis direction between the center of the section 40 c and the center of the magnetic field (Step S109). The control unit 17 then moves the table 4 a in the z-axis direction until the center of the section 40 c matches to the center of the magnetic field based on the measured distance, and stops the move of the table 4 a when they match to each other (Step S110).
In this way, according to the positioning of a scan portion performed by the MRI apparatus 100 according to the first embodiment, after setting the receiving coil 8 onto the subject P, the operator presses a button of a section closest to a region that the operator intends to scan, i.e., a portion that the operator intends to set at the center of the magnetic field, and then only gives an instruction of an automatic slide of the table 4 a by pressing a button on the operation panel 1 b, accordingly, the scan portion is positioned at the center of the magnetic field. In other words, a bothersome positioning operation by using a projector that has been conventionally needed can be omitted.
As described above, according to the first embodiment, the sections 40 a to 40 d included in the receiving coil 8 are provided with the buttons 50 a to 50 d, respectively, and each of the buttons receives from the operator a selecting operation of selecting the section in which the button itself is provided. The control unit 17 of the computer system 10 then moves the table 4 a such that the center of a section selected by receiving a selecting operation via the buttons 50 a to 50 d is positioned at the center of the magnetic field. Consequently, according to the first embodiment, operation of positioning by using a projection light of the projector 1 a is not needed, and even when using a plurality of coils as a coil that receives an MR signal, positioning of a scan portion and the center of the magnetic field can be easily performed. Moreover, a total examination time can be reduced.
Although the first embodiment is explained above in a case of using one section for a scan, the present invention is not limited to this, and can be similarly applied to a case of using two or more sections. A case of using two or more sections is explained below as a second embodiment of the present invention.
A configuration of an MRI apparatus according to the second embodiment is basically similar to that of the MRI apparatus 100 according to the first embodiment, except that a configuration of buttons provided in the sections 40 a to 40 d of the receiving coil 8 and operation of the control unit 17 of the computer system 10 are different. Therefore, a configuration of buttons provided in the sections 40 a to 40 d of the receiving coil 8 according to the second embodiment, and positioning of a scan portion performed by the MRI apparatus 100 according to the second embodiment are explained below.
First of all, a configuration of buttons provided in the sections 40 a to 40 d according to the second embodiment is explained below with reference to FIG. 9. FIG. 9 is a schematic diagram of an appearance of the receiving coil 8 according to the second embodiment. As shown in the figure, the receiving coil 8 according to the second embodiment includes buttons 150 a to 150 d that are provided at respective one ends of the sections 40 a to 40 d, respectively, similarly to the first embodiment.
The buttons 150 a to 150 d receive from the operator a first selecting operation of selecting a section to be positioned at the center of the magnetic field, and a second selecting operation of selecting another section to be used for a scan in addition to the section selected by the first selecting operation, respectively.
Specifically, each of the buttons 150 a to 150 d can take each of three states, namely, a state 1, a state 2, and OFF, instead of each of the two states, ON and OFF only. A transition of the states takes place cyclically each time when each of the buttons 150 a to 150 d is pressed by the operator, and a change of the state is repeated from OFF, the state 1, the state 2, and then to OFF in order, in accordance with the number of times of pressing the button.
When the state of one of the buttons 150 a to 150 d turns to the state 1, the button causes the receiving coil 8 to hold element selection information indicating that the section in which the button itself is provided is a section to be positioned at the center of the magnetic field. On the other hand, when the state of one of the buttons 150 a to 150 d turns to the state 2, the button causes the receiving coil 8 to hold element selection information indicating that the section in which the button itself is provided is selected as a section to be used for a scan.
Furthermore, similarly to the first embodiment, the buttons 150 a to 150 d are provided with indicators 160 a to 160 d, respectively. FIG. 9 is a schematic diagram that depicts indicators according to the second embodiment. As shown in the figure, according to the second embodiment, each of the indicators 160 a to 160 d gives notice of a section to be positioned at the center of the magnetic field, and another section to be additionally used for a scan, in a distinguishable manner.
Specifically, the indicators 160 a to 160 d can take each of three states, namely, a state 1 that it lights up in a first color (for example, red), a state 2 that it lights up in a second color (for example, blue), and a state of light-out, instead of each of only two states, light-up and light-out only. For example, when the button 150 a turns to the state 1, the indicator 160 a lights up in the first color (the state 1); when the button 150 a turns to the state 2, the indicator 160 a lights up in the second color (the state 2); and the button 150 a turns to the OFF state, the indicator 160 a lights out.
In this way, as the indicators 160 a to 160 d switch indications in accordance with respective states of the buttons 150 a to 150 d, the operator can easily confirm a section (or an element) to be positioned at the center of the magnetic field, and a section (or an element) to be used for a scan.
Positioning of a scan portion performed by the MRI apparatus 100 according to the second embodiment is explained below. FIG. 10 is a flowchart of a flow of positioning of a scan portion performed by the MRI apparatus 100 according to the second embodiment. Explained below is a case where the section 40 c is to be positioned at the center of the magnetic field, and the section 40 b is to be used for a scan in addition to the section 40 c.
As shown in the figure, according to the MRI apparatus 100 according to the second embodiment, to begin with the receiving coil 8 is set on a scan portion of the subject P by the operator (Yes at Step S201). An element to be positioned at the magnetic field center is then selected by the operator by pressing a button of a section positioned at the center of a region intended to be scanned in the subject P. In this case, the section 40 c is selected by pressing the button 150 c once by the operator.
When the section 40 c to be positioned at the magnetic field center is selected (Yes at Step S202), the indicator 160 c of the selected section 40 c turns to the state 1, and lights up in the first color (Step S203).
Subsequently, another element to be used for a scan is selected by the operator by pressing a button of another one of the elements twice. In this case, the section 40 b is selected by pressing the button 150 b twice by the operator.
When the section 40 b is selected as a section to be used for the scan (Yes at Step S204), the indicator 160 b of the selected section 40 b turns to the state 2, and lights up in the second color (Step S205).
Subsequently, when an instruction of an automatic slide of the table 4 a is given by pressing a button on the operation panel 1 b by the operator (Step S206), the control unit 17 of the computer system 10 requests the receiving coil 8 for element selection information. Accordingly, element selection information is transferred from the receiving coil 8 to the control unit 17 via the interface unit 11 (Step S207).
When the element selection information is transferred, the control unit 17 controls the switch 20 such that only the coils of the elements included in the sections 40 c and 40 b are turned capable to receive signals, based on the element selection information. Accordingly, the coils of the elements included in the sections 40 c and 40 b are turned to a state selected as an element to receive an MR signal.
Subsequently, the control unit 17 starts moving the table 4 a in the z-axis direction (the longitudinal direction of the table 4 a) by controlling the couch control unit 5 (Step S208), and receives an MR signal of the subject P from the elements included in the selected sections 40 c and 40 b. (Step S209).
After that, when receiving an MR signal from which the center position of the section 40 c can be measured (Yes at Step S210), the control unit 17 measures a distance in the z-axis direction between the center of the section 40 c and the center of the magnetic field (Step S211). The control unit 17 then moves the table 4 a in the z-axis direction until the center of the section 40 c matches to the center of the magnetic field based on the measured distance, and stops the move of the table 4 a when they match to each other (Step S212).
As described above, according to the second embodiment, each of the buttons 150 a to 150 d receives from the operator the first selecting operation of selecting a section to be used for a scan and to be positioned at the center of the magnetic field, and the second selecting operation of selecting another section to be used for the scan in addition to the section selected by the first selecting operation. The indicators 160 a to 160 d distinguishably indicate a section selected by receiving the first selecting operation and another section selected by receiving the second selecting operation, via the buttons 150 a to 150 d, respectively. Consequently, according to the second embodiment, elements included in two or more sections can be used for a scan, and selected sections can be easily confirmed.
Moreover, according to the second embodiment, coils of elements included in sections that are not selected by the operator (the sections 40 a and 40 d) are in a state of not receiving MR signal, so that interference of unwanted signal of other than the region of interest can be reduced, consequently, an image with less artifact can be obtained, compared with a case of receiving signals from the coils of the all elements.
A procedure of selecting a section is not limited to the one described above, and can be configured such that, for example, all sections to be used for a scan are selected by pressing a button once at first; then a section to be set at the center of the magnetic field is selected by further pressing a button once.
Otherwise, a button for specifying a section to be set at the center of the magnetic field and a button for specifying a section to be used for a scan can be separately provided in each section. The indicator is not limited to a multicolor Light Emitting Diode (LED), and can be configured to include two LEDs that indicate the state 1 and the state 2 respectively.
Although the above embodiments are explained in a case where an indicator is provided on an element at one end of each of the sections 40 a to 40 d, it can be configured such that the surface of an element is caused to emit light, for example. FIGS. 11 and 12 are schematic diagrams of a case where the surfaces of elements are caused to emit light.
In such case, for example, as shown in FIG. 11, the whole sensitive region of an element (coil) is caused to emit light by using a surface light-emitting element, such as an organic electroluminescent as an indicator. Accordingly, a reception sensitive region of elements (coils) to be used for a scan can be recognized by the operator more clearly. Alternatively, for example, as shown in FIG. 12, it can be configured such that under a state that the elements are selected, the color or strength of light emission is changed in accordance with a spatial distribution of reception sensitivities of the elements (coils). Accordingly, the coils can be set on the subject more precisely.
The embodiments are explained above in a case of selecting coils by section, i.e., a case where the buttons 50 a to 50 d are provided section by section on the receiving coil 8, and the control unit 17 moves the table 4 a in z-axis direction (the longitudinal direction). However, the present invention is not limited to this. For example, if the MRI apparatus 100 includes a mechanism that can move the table 4 a not only in the z-axis direction but also in the x-axis direction (the crosswise direction), a coil can be selected by element.
In such case, a button is provided on each element on the receiving coil 8, and the control unit 17 moves the table 4 a in the z-axis direction and x-axis direction such that an element selected by the operator is to be positioned at the center of the magnetic field.
According to such configuration, the operator can selects an element to be positioned at the center of the magnetic field from among a plurality of elements arranged in the x-axis direction. Accordingly, for example, when performing a scan of a heart, the operator can position the heart to be a scan portion at the center of the magnetic field easily and accurately, by selecting an element closest to the heart after setting the receiving coil on the subject.
Moreover, the embodiments are explained above in a case of using a receiving coil for abdomen; however, the present invention is not limited to this, and can be similarly applied to a case of using a receiving coil for other than abdomen. For example, a case where the present invention is applied to an MRI apparatus that includes a receiving coil arranged on the back side of a subject is explained below. Such receiving coil is used when scanning, for example, a spine.
FIG. 13 is a schematic diagram of a receiving coil .arranged on the back side of a subject. A receiving coil 80 shown in the figure is implemented by embedding a plurality of coils in a table, and divided into a plurality of elements coil by coil. As shown in the figure, according to the receiving coil 80, similarly to the receiving coil 8 for abdomen as explained above, a plurality of buttons 80 a to 80 h is arranged in the z-axis direction.
A case where coils are embedded in a table as shown in the figure, or a case where a coil for spine that can be placed by moving in the z-axis direction is installed on a table is conceivable as a receiving coil arranged on the back side of a subject.
When the receiving coil is embedded in the table, or when the coil for spine cannot be installed at other than a specific position on the table, as the operator just selects an element to be positioned at the center of the magnetic field, so that a distance between the center of the magnetic field and the element to be positioned at the center of the magnetic field is settled. Therefore, in such case, there is no need to measure the distance by receiving an MR signal.
On the other hand, when the coil for spine can be installed at an arbitrary position in the z-axis direction, similarly to the case of the coil for abdomen explained in the first embodiment, positioning can be performed according to a method of measuring a distance between the center of the magnetic field and the element by receiving an MR signal.
Furthermore, the embodiments are explained above in a case where the receiving coil includes a plurality of elements; however, the present invention is not limited to this, and can be similarly applied to a case where a receiving coil includes only one element, or a case where only one array of elements is arranged in the z-axis direction.
FIG. 14 is a schematic diagram of an example of a receiving coil that includes only one array of elements in the z-axis direction. The figure depicts a case where a receiving coil for shoulder (hereinafter, “shoulder coil”) 90 is set on the right shoulder of the subject P. In this case, it is assumed that the shoulder coil 90 is arranged only one in the z-axis direction. Even in such case, for example, as shown in FIG. 13, an element that can receive an MR signal is sometimes arranged on the table 4 a on which the subject P is placed, in some cases.
In such case, to select the shoulder coil 90 to be actually used by distinguishing from another element arranged on the table 4 a, a button 90 a for selection is provided also on the shoulder coil 90. Regarding positioning of the subject P, even when positional relation between the shoulder coil 90 and the table 4 a is not fixed, similarly to the first embodiment, the shoulder coil 90 can be moved to the center of the magnetic field by using an MR signal from the shoulder coil 90 without positioning operation by using a projector.
Moreover, the embodiments are explained above by assuming a case where the couch 4 is fixed on a gantry of the static magnetic-field magnet 1; however, the present invention is not limited to this, and can be similarly applied to a case where the couch 4 is detachable to the gantry of the static magnetic-field magnet 1. In such case, an element to be positioned at the center of the magnetic field and an element to be used for a scan can be set in advance outside an examination room, so that a total examination time can be reduced.
Furthermore, the embodiments are explained above in a case of using a button as a unit for receiving a selecting operation of selecting an element (or section) from an operator; however, the present invention is not limited to this. For example, when a connector for connecting the receiving coil to the main body of the MRI apparatus is provided on each element, the control unit 17 monitors connection conditions of the connectors, and performs positioning processing on an element of which connector is connected as a selected element.
Moreover, the embodiments are explained above in a case of selecting an element closest to a scan portion after setting the receiving coil on a subject; however, the present invention is not limited to this. For example, in a case of selecting an element of the receiving coil when setting scanning conditions, it can be configured such that the indicator of a selected element preliminarily lights up before the receiving coil is set on the subject.
In such case, for example, the computer system 10 transmits element selection information indicating the element selected by the operator while setting the scanning conditions to the receiving coil via a connector. The receiving coil then causes the indicator of the selected element to lights up based on the transmitted element selection information. For example, when a wireless transmitting unit is provided in each of the computer system 10 and the receiving coil, it can be configured such that the computer system 10 transmits element selection information to the receiving coil via wireless transmission.
Usually, the static magnetic-field magnet 1 and the couch 4 are often installed in a different room from the computer system 10 in many cases. For this reason, the operator sometimes forgets which element is selected in some cases, while the operator is moving to the room in which the static magnetic-field magnet 1 and the couch 4 are installed after setting scanning conditions by using the computer system 10. In such case, if the indicator of a selected element preliminarily lights up, the operator can set the receiving coil at an appropriated position on the subject without mistaking the selected element.
The embodiments are explained above in a case of selecting an element (or section) of the receiving coil by turning a button to the ON state by the operator. However, for example, there is a possibility that the operator forgets to turn the button of a coil used for a scan to the OFF state, when the scan is finished. In such case, it is conceivable that an unexpected element is positioned at the center of the magnetic field in the next scan, or that an unexpected element is used for the next scan.
Therefore, for example, it can be configured to cancel automatically at a certain moment a state that an element is selected. In such case, for example, at a moment after the control unit 17 of the computer system 10 has moved the table 4 a until an element selected by the operator is positioned at the center of the magnetic field, the control unit 17 turns off the button of the selected element, and deletes the element selection information held by the receiving coil.
Alternatively, for example, at a moment when the control unit 17 of the computer system 10 starts moving the table 4 a after acquiring element selection information from the receiving coil, the control unit 17 can turn off the button of the selected element, and can delete the element selection information held by the receiving coil.
Accordingly, even if the operator forgets to turn the button of a coil used for a scan to the OFF state when the scan is finished, a mistake of positioning an unexpected element at the center of the magnetic field in the next scan, or a mistake of using an unexpected element for the next scan can be avoided.
Furthermore, the second embodiment is explained above in a case where the first selecting operation of selecting a section to be used for a scan and to be positioned at the center of the magnetic field, and the second selecting operation of selecting another section to be used for the scan in addition to the section selected by the first selecting operation are received respectively, and then the table is moved such that the section selected by receiving the first selecting operation is to be positioned at the center of the magnetic field.
However, for example, when using a plurality of sections (or elements) for a scan, the table can be moved such that the center of the whole of the sections selected by the operator is to be positioned at the center of the magnetic field.
In such case, for example, the storage unit 14 of the computer system 10 preliminarily stores information about positional relation of sections (or elements) included in a receiving coil as coil information with respect to each type of receiving coils. Moreover, the control unit 17 detects the type of a receiving coil when the receiving coil is connected to a connector. When an MR signal is received by selected sections as assumed to be used for a scan, the control unit 17 calculates a distance in the z-axis direction between the center of the whole of the selected sections and the center of the magnetic field, by referring to the coil information stored in the storage unit 14. The control unit 17 then moves the table 4 a in the z-axis direction until the center of the whole of the selected sections matches to the center of the magnetic field based on the measured distance.
Accordingly, when an odd number of sections are selected by the operator, the center of a section positioned at the center of the selected sections is positioned at the center of the magnetic field. By contrast, when an even number of sections are selected, the middle of two sections positioned at the center of the selected sections is positioned at the center of the magnetic field.
Moreover, in this case, any button that can take two states of ON and OFF can be used as a button for selecting a section instead of using a button that can take three states, the state 1, the state 2, and OFF, as described in the second embodiment, and the center of the whole of the sections is automatically positioned at the center of the magnetic field only by selecting sections to be used for a scan by the operator. Accordingly, when using a plurality of sections for a scan, positioning of a scan portion and the center of the magnetic field can be more easily performed.
As described above, the magnetic resonance imaging apparatus and the control method of the magnetic resonance imaging apparatus according to the embodiments of the present invention are useful when a plurality of receiving coils or a receiving coil including a plurality of elements is used for scan, and particularly suitable when a total examination time is required to be reduced by reducing operations required for positioning a scan portion.
Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

Claims

1. A magnetic resonance imaging apparatus comprising:

a plurality of coils that receives a magnetic resonance signal irradiated from a subject;

a receiving coil that includes the plurality of coils;

a coil selecting unit that is provided in the receiving coil, and receives from an operator a selecting operation of selecting a coil from among the plurality of coils; and

a control unit that moves a table on which the subject is placed such that the coil selected by receiving the selecting operation by the coil selecting unit is positioned at a center of a magnetic field.

2. The apparatus according to claim 1, further comprising a selected-coil notifying unit that gives notice of a coil selected by receiving the selecting operation by the coil selecting unit.

3. The apparatus according to claim 1, wherein

the coil selecting unit receives from the operator a first selecting operation of selecting a coil to be used for a scan and to be positioned at the center of the magnetic field, and a second selecting operation of selecting a coil to be used for the scan in addition to the coil selected by the first selecting operation, and

the control unit moves the table such that the coil selected by receiving the first selecting operation by the coil selecting unit is positioned at the center of the magnetic field.

4. The apparatus according to claim 3, further comprising a selected-coil notifying unit that gives notice of the coil selected by receiving the first selecting operation by the coil selecting unit, and the coil selected by receiving the second selecting operation by the coil selecting unit in a distinguishable manner.

5. The apparatus according to claim 2, wherein the selected-coil notifying unit changes a mode of notice in accordance with one of a sensitive region and a spatial distribution of sensitivity of the coil selected by receiving the selecting operation.

6. The apparatus according to claim 4, wherein the selected-coil notifying unit changes a mode of notice in accordance with one of a sensitive region and a spatial distribution of sensitivity of the coil selected by receiving the selecting operation.

7. The apparatus according to claim 1, wherein the control unit measures positional relation between the center of the magnetic field and the coil selected by receiving the selecting operation based on a magnetic resonance signal received by the coil, and moves the table based on the measured positional relation.

8. The apparatus according to claim 2, wherein the control unit measures positional relation between the center of the magnetic field and the coil selected by receiving the selecting operation based on a magnetic resonance signal received by the coil, and moves the table based on the measured positional relation.

9. The apparatus according to claim 3, wherein the control unit measures positional relation between the center of the magnetic field and the coil selected by receiving the selecting operation based on a magnetic resonance signal received by the coil, and moves the table based on the measured positional relation.

10. The apparatus according to claim 4, wherein the control unit measures positional relation between the center of the magnetic field and the coil selected by receiving the selecting operation based on a magnetic resonance signal received by the coil, and moves the table based on the measured positional relation.

11. The apparatus according to claim 5, wherein the control unit measures positional relation between the center of the magnetic field and the coil selected by receiving the selecting operation based on a magnetic resonance signal received by the coil, and moves the table based on the measured positional relation.

12. The apparatus according to claim 1, wherein

the receiving coil includes the plurality of coils that are arranged in parallel along a longitudinal direction of the table, and

the control unit moves the table along the longitudinal direction.

13. The apparatus according to claim 2, wherein

the control unit moves the table along the longitudinal direction.

14. The apparatus according to claim 3, wherein

the control unit moves the table along the longitudinal direction.

15. The apparatus according to claim 4, wherein

the control unit moves the table along the longitudinal direction.

16. The apparatus according to claim 1, wherein

the receiving coil includes the plurality of coils that are arranged in parallel along a crosswise direction of the table, and

the control unit moves the table along the crosswise direction.

17. The apparatus according to claim 2, wherein

the control unit moves the table along the crosswise direction.

18. The apparatus according to claim 3, wherein

the control unit moves the table along the crosswise direction.

19. The apparatus according to claim 4, wherein

the control unit moves the table along the crosswise direction.

20. A method of controlling a magnetic resonance imaging apparatus, the method comprising:

receiving from an operator a selecting operation of selecting at least one coil from among a plurality of coils included in a receiving coil that receives a magnetic resonance signal irradiated from a subject, and

moving a table on which the subject is placed such that the coil selected by receiving the selecting operation is positioned at a center of a magnetic field.